1. Field of the Invention
This invention relates generally to a method and apparatus for collecting breath samples from humans and, in particular, is directed to an uncomplicated, user-friendly and relatively inexpensive apparatus and method for collecting such breath samples such that they consist primarily of alveolar gas as expelled from the pockets of the lungs.
2. Description of the Prior Art
Certain diagnostic techniques require analysis of the breath of a human subject to determine whether the breath contains a particular chemical compound, such as ethyl alcohol, carbon dioxide or ammonia, or a non-chemical, such as a particular microorganism. Determining the constituent components of the breath is best accomplished by analyzing the alveolar gas, that is the portion of the exhaled breath which is expelled from the air pockets of the lungs. In exhalation, as the lungs contract, breath contained in the mouth, throat and bronchials is necessarily exhaled first, followed by the breath contained in the alveoli of the lungs. Since it is at the alveoli where the exchange of substances between breath and blood ultimately occurs, the concentration of gaseous or vaporous constituents in the alveoli corresponds more closely to the concentration of substances dissolved in the blood. Thus, if a sample of breath is to be analyzed for the presence of constituents which may be present in the blood, the sample of breath analyzed must be at least primarily alveolar gas.
The equipment commonly used for collecting alveolar breath samples consists of bags, valves, syringe and needles and evacuated containers such as used for blood samples. These devices are expensive and complex which makes them very difficult for a patient to use. For example, U.S. Pat. No. 3,734,692 discloses an alveolar breath sampling apparatus utilizing a complicated compartm.entalized bag having first and second inflatable regions. A dual channeled delivery port is constructed into the apparatus and communicates with both regions. The breath sample is collected by breathing into the delivery port resulting in the sequential collection in each region. This device is unnecessarily complex and expensive to construct.
In another known arrangement, the alveolar air portion of a person's breath is separated in response to the temperature of the conveyed air. For example, U.S. Pat. No. 4,248,245 discloses a method and device for separating alveolar air which includes conveying the exhaled air through a conduit and continuously monitoring the temperature of the conveyed air. When the variation in measured temperature drops below a threshold value, the air is directed into a measuring chamber. This device is also excessively complex and expensive to manufacture.
In still another prior art arrangement, two separate collection bags are used interconnected by a conduit. For example, in U.S. Pat. No. 3,544,273, a first collection bag and a second collection bag are connected by a T-shaped conduit having one branch formed into a mouth piece. The breath sample is collected by inflating the first bag with the initial breath poriton and filling the second bag with the alveolar air. The second bag is sealed by using a valve structure. The complexity of these devices and resultant difficulty individual users have in operating them has often resulted in less than accurate measurements. In addition, such prior art systems are intimidating to the user and difficult to use in any event and thus are not as widely used as considered medically prudent for early diagnostic purposes.
Thus, there is a great need for an accurate, inexpensive and most importantly user friendly method and apparatus for collecting a human breath sample, primarily the alveolar portion thereof, for the analysis of the constituent components thereof.